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Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
1
Big Bang, Black Holes, No Math
ASTR/PHYS 109Dr. David Toback
Lectures 19,20 & 21
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
Was due Today – L21• Reading:
– (Unit 2) • Pre-Lecture Reading Questions Quiz:
– (Unit 2 Text Submission and Unit 2 Quiz)• End-of-Chapter Quizzes:
– (Chapter 7a and 7b)• Papers
– Paper 1:• Text was due already in Peerceptive and TurnItIn (in eCampus) on Friday Feb
21st
• Please finish your Reviews if you haven’t done so already. Your fellow classmates cannot get a grade until they have 3 Reviews to Back-Evaluate
• If you want to do a revision, send me an email– Paper 2:
• Text: Currently set for Monday March 9th– Submit to Peerceptiv AND TurnItIn
• Draft for Feedback (Optional) – Currently due Wednesday March 4rd
– Will do our best for late submissions • Reviews and Back-evaluations: Same as before
3
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
Heads Up: Paper 2• What is the evidence that Stars are made of Atoms?
• This will be the topic of Paper 2
• In order to understand the evidence, we next talk about Atoms and how they work
• Will be assigned after we finish Chapter 8
4
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
5
Outline for Unit 2: Physics We Need
1. Light and Doppler Shifts Done2. Gravity, General Relativity and
Dark MatterDone3. Atomic Physics and Quantum
Mechanics Done4. Nuclear Physics and Chemistry
This time5. Temperature and Thermal
Equilibrium
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
Clicker QuestionA neutral helium atom is sitting in space when a photon hits it. Depending on the photon energy, the following things can happen:A. An electron gets knocked out and the atom becomes ionizedB. A proton gets knocked out and it become a hydrogen atomC. A quark gets knocked out of the protonPlace the following in order from highest required energy to
lowest: a) A>B>Cb) A>C>Bc) B>A>Cd) C>A>Be) C>B>A
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Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
Unique Fingerprints
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• Look at light from a light bulb with Hydrogen gas in the way
• Different lines will be absorbed by Helium
• Can now identify a mystery gas!
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
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Overview of the story• Big things are made from LOTS of small things • Small things: The Fundamental Building Blocks of Nature
– What is the “stuff” in atoms• ElectroMagnetism (electric charge)
– What holds electrons and protons together• Quantum Mechanics
– Why atoms form the way they do– Electron in orbits– Atoms absorbing and emitting photons (light)
• Different TYPES of Atoms– The Strong Force– Keeping protons and neutrons together (atomic nuclei)– Nuclear Physics and Chemistry– Different atoms Different light…
• Studying the Stars using their light– Spectral lines of the atoms – Atomic “fingerprints”– The light we see from the stars
LastLecture
ThisLecture
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
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Learning about Stars from their Light•Can look at the light from the stars to learn about them•Are they made of atoms?•If so, what TYPE of atoms? •How are stars formed?•What makes them shine?
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
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What is a Star?
• Our best understanding is that stars are giant balls of (mostly) hydrogen atoms
• The hydrogen interacts and produces the light we see– Makes them shine…
• What is the evidence for this?
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
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Stars• What would happen inside a giant ball of hydrogen?– Atoms would fall to the center (due to gravity) and bash into each other
• What would that look like to us?– Light from their interactions
– Next look at interactions
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
Proton + Proton Deuterium + Anti-Electron + Neutrino
Hydrogen Interactions produce energy
Proton
Proton
DeuteriumNuclear Reaction
Anti-Electron
Neutrino
The Deuterium, neutrino and the Anti-Electron get energy in the reaction26
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
Where does the energy come from?
•Mass of Deuterium is smaller than the mass of two protons
• So what? E=mc2, so the “mass energy” gets converted into kinetic energy in the collision (and light)
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Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
Proton + Deuterium Helium3 + Photon
More interactions More Energy
Deuterium
Proton
Helium3
Nuclear Reaction
Photon
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Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
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Helium3 + Helium3 Helium4 + 2 Protons
Creating Stable Helium produces more…
Helium3
Helium3
Helium4
Nuclear Reaction
Proton
Proton
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
30
Stars Shining
•Nuclear interactions in the center of the star create lots of energy which is eventually emitted as light from the surface of the star–Shines white (or yellow)
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
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What else can we learn from the light?
•This light passes through other atoms of the star–Light is “absorbed” by the outer atoms Spectral lines
•Tells us what the stars are made of
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
Looking at the Stars
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Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
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Analyzing Absorption Spectra• Each element produces a specific set of absorption (and emission) lines
• Using this information, we can study the composition of stars
See only spectral lines for known atoms
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
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Remarkable…• The Sun and stars are mostly made of Helium and Hydrogen
• Our Sun is made of the same stuff as all the other stars!
• The stuff out in the universe is made of the same stuff that is found here on Earth!
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
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Even More RemarkableIf all the stuff “out there” looks the same as the stuff here on Earth then: –The particles out there (electrons, protons, photons etc.) are the same as they are here
–The laws of physics that govern putting together protons, nuclei and atoms are likely to be the same everywhere!
–Strong evidence that the laws of physics have been the same for billions of years!
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
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Now that we know what stars are made of and
what they are SUPPOSED to look like, can we learn
anything else?
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
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•What if the stars were MOVING? •Can we tell? Yes!
Doppler effectHow?
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
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Atoms with Different Speeds
• If an atom emits a photon it will correspond to an energy that reflects the change of two energy levels
• However if the atom is MOVING the light will be shifted to a different color
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
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Observing an Atom
Atom Emitting Light
Not MovingMoving to the right
Can use this to study the motions of the stars
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
Looking at the Stars
40
Provides additional evidence stars are made
of atoms
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
Lecture on Chapter 8 now complete
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Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
Paper 2
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• Abbreviated description: What is the evidence that Stars are made of Atoms? – More detail on Peerceptiv, you REALLY need to
read ALL the instructions• Explain it to someone who isn’t taking the class (no
jargon)• Format:
– Introduction paragraph • Lawyers opening arguments at a Trial
– ~1 paragraph per piece of evidence/talking point• The case at a Trial
– Conclusion paragraph that ties it together• Lawyers closing arguments at a Trial
http://people.physics.tamu.edu/toback/109/WritingAssignments/samplepaper.shtml
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
43
Outline for Unit 2: Physics We Need
1. Light and Doppler Shifts Done2. Gravity, General Relativity and
Dark Matter Done3. Atomic Physics and Quantum
Mechanics Done4. Nuclear Physics and Chemistry
Done5. Temperature and Thermal
Equilibrium Next time
Physics We NeedTopic 4: Nuclear Physics & Chemistry
Big Bang, Black Holes, No Math
Prep For Next Time – L21• Reading:
– (Unit 2) • Pre-Lecture Reading Questions Quiz:
– (Unit 2 Text Submission and Unit 2 Quiz)• End-of-Chapter Quizzes:
– If we finished Chapter 8 then End-of-Chapter Quiz parts 8a and 8b (else, just 7a and 7b)
• Papers– Paper 1:
• Text was due already in Peerceptive and TurnItIn (in eCampus) on Friday Feb 21st
• Please finish your Reviews if you haven’t done so already. Your fellow classmates cannot get a grade until they have 3 Reviews to Back-Evaluate
• If you want to do a revision, send me an email– Paper 2:
• Text: Currently set for Monday March 9th– Submit to Peerceptiv AND TurnItIn
• Draft for Feedback (Optional) – Currently due Wednesday March 4rd
– Will do our best for late submissions • Reviews and Back-evaluations: Same as before
48
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